fix(@schematics/angular): validate project name before prompts
fix(@schematics/angular): validate project name before prompts

When an invalid project name is given, throw an error before going through prompts.

Closes #14994

ocombe/angular-cli,catull/angular-cli,geofffilippi/angular-cli,Brocco/angular-cli,catull/angular-cli,angular/angular-cli,catull/angular-cli,Brocco/angular-cli,ocombe/angular-cli,angular/angular-cli,clydin/angular-cli,Brocco/angular-cli,clydin/angular-cli,ocombe/angular-cli,geofffilippi/angular-cli,geofffilippi/angular-cli,Brocco/angular-cli,ocombe/angular-cli,catull/angular-cli,angular/angular-cli,Brocco/angular-cli,clydin/angular-cli,clydin/angular-cli,geofffilippi/angular-cli,ocombe/angular-cli,angular/angular-cli